Implantable electrical stimulation has proven therapeutic in a variety of diseases and disorders. For example, spinal cord stimulation systems have been used as a therapeutic modality for the treatment of chronic pain syndromes. Peripheral nerve stimulation has been used to treat chronic pain syndrome and incontinence, with a number of other applications under investigation. Functional electrical stimulation systems have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Stimulators have been developed to provide therapy for a variety of treatments. A stimulator can include a control module (with a pulse generator), one or more leads, and an array of stimulator electrodes on each lead. The stimulator electrodes are in contact with or near the nerves, muscles, or other tissue to be stimulated. The pulse generator in the control module generates electrical pulses that are delivered by the electrodes to the body tissue.
Conventional implanted electrical stimulation systems are often incompatible with magnetic resonance imaging (“MRI”) due to the large radio frequency (“RF”) pulses used during MRI. The RF pulses can generate transient signals in the conductors and electrodes of an implanted lead. These signals can have deleterious effects including, for example, unwanted heating of the tissue causing tissue damage, induced currents in the lead, or premature failure of electronic components.
When patients implanted with, or example, deep brain stimulation (DBS) or cardiac pacing (CP) lead systems are exposed to external Radio Frequency (RF) fields, local tissue damage around the electrodes of these leads can occur. During an MRI scan, the transmit RF field generates current along the conductors within an implanted lead. The current is then delivered through the conductors and into the surrounding tissue. Where the current emerges from the electrodes coupled to the conductors, it can be concentrated and can cause heating and subsequent tissue damage.